1. Field of the Invention
The invention relates to a laser, and more particularly to a thin-disk solid state laser.
2. Description of the Related Art
With continuous development in laser technology, solid state laser has become a unique branch in the laser family with its incomparable merits. It develops by leaps and bounds to make higher achievement in average power, beam quality, and conversion efficiency. Meanwhile, the inter-penetration between solid state laser technology and other high and new technologies enables the solid state laser to be more widely applied in such fields as shell plate welding on auto body, tailor welding of auto plate, and metal plate cutting. However, traditional rod solid state laser has limitations on the structure of lateral pump and cooling method. These limitations may lead to distribution of radial temperature field within the crystal, bring in such problems as thermal lens effect and double refraction of thermal stress, cause a drop on the quality of output laser beam, and restrict the application of laser in laser processing technical field.
The thin-disk solid state laser mainly makes use of thin-disk laser crystal as the gain medium. Generally, end pump is adopted and the direction of heat flow is parallel to the direction of optical axis. Since laser crystal is thin, the temperature increase within the crystal will not be so dramatic even under extremely high density of pump power. The even temperature distribution within the crystal enables it to produce high-quality laser beam.
Both high-efficient pump and crystal cooling are key technologies in thin-disk solid state laser. At present, most of thin-disk solid state lasers adopt the plan of multi-pumping in single paraboloid beam space, for this plan achieves perfect effect on the power, efficiency, and beam quality of solid state laser. However, this multi-pumping technology also encounters some problems such as the complex mechanical structure and difficult optical adjustment. Main crystal plan refers to the cooling plan with high efficiency, but in this plan, the element processing is really difficult, the assembly space is small and the cooler and pump within the system confronts much higher requirements.
In 2008, a plan about a thin-disk solid state laser with SMD crystal cooling system and multi-pumping structure was proposed, which is based on conjugated double-paraboloid, inclined laser crystal, and corrective reflector. This new plan can realize multi-pumping and disk cooling to some degree, but its main problem is the low efficiency of pump light due to the inclined position of laser crystal. When the laser crystal is placed in an inclined position, only one beam of pump light is permitted to enter the focus cavity and this is unfavorable to gain higher pump efficiency. It is really difficult to adjust the resonant cavity (whose direction is also the output direction of laser) and use the output laser because of the inclined position of laser crystal. Moreover, in this plan, the laser crystal is connected with cooling system through SMD technology. For the immersion jet-flow impact cooling system, its design is difficult, heat transfer efficiency is low, and the assembly is complex.